Nucleic Acid

Nucleic Acid

Deoxyribonucleic acid) This is a polynucleotide, it is made up of nucleotides joined up in a double helix. A single nucleotide is made up of a phosphate group, a deoxyribose sugar which is pentose and a organic nitrogenous base. The phosphate group and pentose sugar link together to form a back bone. Monomer nucleotides can be linked in this way to form a polynucleotide chain. A DNA molecule is made up of 2 polynucleotide chains held together by hydrogen bonds between the bases. The chains and then twisted to form a double helix. There are four possible bases: adenine, thymine, guanine and cytosine. Adenine forms 2 H bonds with thymine and cytosine bonds 3 H bonds with guanine. The two bonds are anti parallel as one strand is a pentose sugar pointed up then phosphate while the other strand is sugar pointing down - phosphate. Bases are either be purines or pyramidines. Purines are thymine and cytosine as they have two carbon rings while pyramidines are adenine and guanine as they have one carbon ring. This means that purines always matches pyramidines so the distance between the two strands are constant.

Ribonucleic acid) This is also a nucleic acid made up of nucleotides. However unlike DNA there is only a single strand, the thymine base is also replaced by uracil. There is also ribose sugar present instead of deoxyribose.

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Protein Synthesis

Semi-conservative

During cell division the DNA molecule has to be copied, one method of doing this is called semi conservative replication. This is done by the molecule first unwinding due to the DNA helicase enzyme. The hydrogen bonds then break between the bases the two strands then separates. The strands then work as templates to bring free nucleotides to form a complementary strand with the complementary bases. The DNA polymerase enzyme then combines the nucleotides and the end result are two identical DNA molecules

Protein Synthesis

DNA is a collection of genes used to make proteins for the body, these protein are made of amino acids. Three bases (a triplet code) makes a amino acid.

Transcription) The DNA double helix unwinds, MRNA then attaches and forms the complementary bases, the MRNA is able to move in and out of the nucleus as it is only one strand.

Translation) The MRNA leaves the nucleus and attaches to a ribosome and is read by TRNA, it reads the triplet codes and brings the correct amino acids in the right order to make protein